1. Field of the Invention
The present invention relates, in general, to surface mountable light-emitting diode devices. More specifically, the present invention is directed to a method of manufacturing a light-emitting diode device, capable of simply forming reflective surfaces made of a metal material by use of a lead frame.
2. Description of the Related Art
As well known to those skilled in the art, a light-emitting diode (hereinafter, referred to as ‘LED’) composed of a compound semiconductor, such as GaAs, AlGaAs, GaN, InGaN or AlGaInP, as a light-emitting source, is a semiconductor device capable of emitting light of various colors.
With great advances in semiconductor techniques, LED devices have recently been produced to have high luminance and quality characteristics, in place of commercially available LED products with low luminance. In addition, fabrication of blue and white diodes has been practically realized, whereby the LEDs are widely applicable to displays, next-generation lighting sources and the like. For instance, a surface mountable LED device is available.
FIG. 1 schematically shows the surface mountable LED device, comprising a package molded with an epoxy resin. A certain surface of the package 2 is formed to an open window 4 so as to easily emit light, and the other surfaces are attached with electrodes 5 so as to be mounted in a printed circuit board 1. In the package 2, a light-emitting surface of an LED chip is disposed to face to the light-emitting window 4, and the electrodes 5 are connected with the LED chip by a wire.
Factors determining the characteristics of the LED device include color, luminance, strength of luminance, etc. While the characteristics of such an LED device mainly depend on a compound semiconductor material used for the LED chip, they are further affected by a structure of the package for use in mounting the LED chip. The LED package structure has an influence on luminance and luminance angle distributions.
The surface mountable LED package suffers from low luminance due to a broad luminance distribution.
FIG. 2 shows a structure of a conventional surface mountable LED device. As shown in FIG. 2, the LED device comprises a lead frame 21, a package 22 formed by a pre-molding process to contain a portion of the lead frame 21, an LED chip 23 mounted on the lead frame 21 in the package 22, and a molding material 25 filled in the package 22 to protect the LED chip 23.
With reference to FIGS. 3a through 3e, there is shown a process of manufacturing such a conventional LED device, comprising forming a lead frame (FIG. 3a), plating (FIG. 3b), pre-molding (FIG. 3c), mounting a chip and wire-bonding (FIG. 3d), and filling epoxy (FIG. 3e). In such a case, the lead frame 31 includes a first pattern part 31a for use in mounting an LED chip thereon, a second pattern part 31b integrated with the first pattern part 31a for use in an electrode, and a third pattern part 31c spaced from the first pattern part 31a so as to be electrically insulated from the first pattern part 31a. On a front surface of the lead frame 31, a metal-plated layer 32 having high adhesion and conductivity is formed to easily perform a wire-bonding process. In FIG. 3c illustrating the pre-molded state, a hexahedron-shaped package 33 having an inner cavity is formed to surround the other portions of the lead frame 31 with the exception of electrode portions of the second and third pattern parts 31b and 31c of the lead frame 31 to be used as external electrodes. An LED chip 34 is mounted on the first pattern part 31a of the lead frame 31 in the package 33, and the LED chip 34 is wire-bonded to each of the second and third pattern parts 31b and 31c in the package 33 to form wire-bonded portions. As shown in FIG. 3e, the package 33 is filled with transparent epoxy 36 to protect the LED chip 34 and the wire-bonded portions.
However, such an LED device is disadvantageous in terms of characteristic deterioration and decreased functions, resulting from defects of crystals caused by artificial growth in the compound semiconductor, serving as the emitting source. Further, packaging and transparent molding materials may be degraded in characteristics thereof, too.
As seen in FIG. 2 and FIGS. 3a through 3e, the conventional LED device is low in reflection efficiency, since a plastic material is used at the pre-molding process. Also, upon use of such a device for extended periods, deterioration of the pre-molded package takes place as in molding materials, thus significantly lowering luminance characteristics.
Moreover, the pre-molded package has low thermal conductivity, and is restricted for use in products with high luminance. Additionally, upon emission of light from the LED chip, inner surfaces of the package useful as a light-emission passage are non-uniform, thus lowering reflection efficiency.